The invention relates to a polycarbonate composition with improved melt-flowability together with good optical properties and together with good hydrolysis resistance.
Production of injection-moulded polycarbonate parts, particularly in the case of thin-walled mouldings, requires that melt-flowability is sufficiently high to permit the injection-moulding procedure to proceed in a fully satisfactory manner. Mouldings of this type are exposed to a very wide variety of ambient conditions, as a function of the application sector, and have to provide fully satisfactory compliance here with a wide variety of demands. The polycarbonate therefore in particular has to have the traditional good optical properties, as well as its processing properties. There must moreover be no alteration of these good properties when, as occurs relatively frequently, the material is exposed to moisture, and this requirement extends to relatively high temperature.
A type of polycarbonate that is of increasing economic importance, therefore being a suitable material for many application sectors, is produced in the melt by what is known as the melt transesterification process, also termed the melt process, from organic carbonates, e.g. diaryl carbonates, and bisphenols, without use of additional solvents.
Production of aromatic polycarbonates by the melt transesterification process is known and by way of example is described in “Schnell”, Chemistry and Physics of Polycarbonates, Polymer Reviews, Vol. 9, Interscience Publishers, New York, London, Sydney 1964, in D. C. Prevorsek, B. T. Debona and Y. Kersten, Corporate Research Center, Allied Chemical Corporation, Moristown, N.J. 07960, “Synthesis of Poly(ester)carbonate Copolymers” in Journal of Polymer Science, Polymer Chemistry Edition, Vol. 19, 75-90 (1980), in D. Freitag, U. Grigo, P. R. Müller, N. Nouvertne, BAYER AG, “Polycarbonates” in Encyclopedia of Polymere Science and Engineering, Vol. 11, Second Edition, 1988, pages 648-718 and finally in Des. U. Grigo, K. Kircher and P. R. Müller “Polycarbonate” in Becker/Braun, Kunststoff-Handbuch [Plastics handbook], Volume 3/1, Polycarbonate, Polyacetale, Polyester, Celluloseester [Polycarbonates, polyacetals, polyesters and cellulose esters], Carl Hanser Verlag Munich, Vienna 1992, pages 117-299.
Melt polycarbonates which comprise organic phosphorus compounds, e.g. phosphines, phosphine oxides, phosphinites, phosphonites, phosphites, disphosphines, diphosphinites, diphosphonites, diphosphites, phosphinates, phosphonates, phosphates, diphosphinates, diphosphonates and diphosphate compounds, have been described by way of example in EP-A-1 412 412, and also in JP-08-225736 and JP-11-100497. EP-A-1 412 412 mentions the improved hydrolysis resistance properties of melt polycarbonates modified in this way. However, the disclosures do not contain any indications of an improvement in rheological or optical properties of a polycarbonate.
Melt polycarbonates which comprise aliphatic fatty acid esters have also been widely disclosed in the literature, for example in U.S. Pat. No. 2,004,225047 or EP-A-561 638, which describe the improved demouldability and surface quality of injection-moulded parts made of polycarbonate moulding compositions of this type. No indications of an improvement in rheological or optical properties of the polycarbonate moulding compositions can be found in the said disclosure.
JP 02-219855 describes polycarbonate moulding compositions which comprise trialkyl phosphates and esters of saturated fatty acids, but does not describe combinations with further phosphorus compounds. There are no indications of hydrolysis resistance or of rheological properties. Nor is it possible to discern whether the property improvements mentioned in that document also apply to melt polycarbonates.
EP 561629 contains examples of melt polycarbonate moulding compositions which comprise phosphite and aliphatic fatty acid ester, and which have improved demoulding behaviour. However, the disclosure provides no indications of rheological properties or hydrolysis resistance. However, comparative trials reveal that moulding compositions of this type which comprise phosphite and aliphatic fatty acid ester have markedly impaired hydrolysis resistance, leading to disadvantageous alterations in the optical and mechanical properties of the mouldings produced therefrom.
It was therefore an object of the invention to produce moulding compositions from a melt polycarbonate which has improved processing properties in terms of melt-flowability together with good hydrolysis resistance and good optical properties.